Recently, various apparatuses used in various industrial fields such as automobiles, appliances and machines have been required to have high performances and functions and have been used under increasingly severe conditions. This tendency is especially conspicuous in automobile industries which are largest users for rubbers. For example, the atmosphere in engine rooms tends to be higher in temperature owing to countermeasures against regulation of off-gas or improvement of engines aiming at enhancement of performance such as increase of power output, and rubbers to be employed for such uses are required to be excellent not only in heat resistance, ozone resistance and oil resistance, but also in flexibility at low temperatures, namely, to be well balanced in properties.
Ethylene copolymer rubbers comprising ethylene and at least one membered selected from the group consisting of acrylic esters and methacrylic esters as constituting units are excellent in heat resistance, low-temperature resistance and strength characteristics, but are inferior in oil resistance. In order to solve this problem, an attempt has been made to increase contents of acrylic esters and/or methacrylic esters. However, this method has the problems that molecular weight of ethylene copolymer rubbers decreases and elasticity, which is a characteristic of rubbers, is not sufficiently exhibited and besides, improvement of oil resistance is also insufficient. That is, there have not yet been found rubbers or rubber compositions which are well balanced in properties such as strength characteristics, oil resistance, low-temperature resistance, heat resistance and ozone resistance with maintaining the characteristics of rubbers.